L2 Rocket Design Questions

[haon151]

so many choices it seems. I tend to agree with this approach has well. Another option to this approach you can use a JLCR if you wanted to take it a bit higher?

What is JLCR?

 

[haon151]

Using dual deployment (DD) for your L2 flight is only a big challenge if you make it a big challenge.
Be patient and keep it simple.

I did DD for my L2 flight. I used LOC's EZI-65 kit for my base design. I have attached the design in a PDF file.
This is a 4" dia. rocket, cardboard. I used/use a single RRC2 and 9-volt battery. I've had this rocket for a very
long time, and it's flown on "I" through "K" motors, warp motors too.

The most noticeable change to the basic EZI kit is the 24" long motor tube. I wanted to eventually put the
rocket up on a K1050 motor - which at the time was the only motor AeroTech made for the 2800 case.

View attachment 573534
I've included the drawing so that you can get a feel for the available space for your harnesses and chute.
I use 25 ft. harnesses, 7/16" Kevlar - and I think Teddy (OneBadHawk) made them for me. I use a 50" Top
Flight chute for the Main. The top payload area has all kinds of room.

The GPS tracker is for those launches where the winds are questionable above 4,000 ft. And there are
plenty of motors that keep the altitude under 3,500 ft. - which was the limit on the original field this
was regularly launched on.

There is no drogue chute in the lower payload - for Apogee separation. The 25 ft. harness, along with
a nomex blanket and zipper protection fit snuggly in this lower payload. I wish at times it had another
inch or two of length. But that was sacrificed when I put in the 24" motor tube. Live & Learn.

This kit went back to the days when Barry still owned LOC, and his shop was here in Ohio. This explains
the (2) 11" tubes and coupler to make up the top section. The kit came with one 11" section. When I
decided to go DD I needed to extend the top section - so I just added another 11" tube.

In those days the kit had 1/8" plywood fins. I changed them to 1/4" at the advice of the more
experienced people. Glad I did. I think 1/4" is now standard in the LOC kit.

I have included a couple of pictures of the "avionics" bay. I have to laugh at how simple & barren it
is compared to the avionics bays I now put together.

I spent most of my time on the GPS compartment in the nose cone. I rarely have to use it, it was not
a necessity for the L2 cert. It comes in handy now - but I could have skipped that extra work for my
L2 cert flight. Oh well, Live & Learn.

I'm glad I did the DD for my L2. It gave me the opportunity to learn some good stuff from the
experienced people at the launches - and it built up their confidence, and mine, that I would have
a good first launch. It made the cert flight more fun, along with a greater sense of accomplishment.


View attachment 573536 View attachment 573537

View attachment 573539 View attachment 573540

Thank you for your detailed response and the images. You give me hope that this is a reasonable goal. That gives me an idea on how to adjust the sizing on my rocket as well. What did you use to annotate that drawing?

I see you used 6 centering rings. How did you come up with this number, and do you think I should increase my amount?

 

[haon151]

I would not recommend doing anything for the first time on your L2 flight other than the motor being your first L2 class motor.

If you plan to use dual deploy for your L2 flight then you should absolutely practice dual deployment prior to your cert flight. You can use your L2 rocket for practice however I can see a good reason to not use your L2 rocket the first few times you fly dual deploy. If you mess something up on the first few DD attempts you could damage or completely destroy your L2 bird. I'd recommend practicing dual deployment on another airframe and once you are comfortable do at least one DD shakedown flight with your L2 bird on a L1 motor. Then you will be ready for a cert attempt. That is the safest approach IMO.

Ya I would definitely practice on some lower power motors beforehand.

I see now the overarching consensus is to practice before the cert. Is building something like this too ambitious for a beginner? Like you said I'd rather not destroy the L2 bird on it's maiden flight. How will I know my design is good and will work?

 

[tsmith1315]

What is JLCR?

An altimeter-based Chute Release, which keeps the parachute bundled until you want it to open at a specified altitude.

You can use it with motor ejection or with a simple altimeter like the Eggtimer Apogee, to get the bundled chute out into the air.

Either way, it's still a learning curve that should be practiced beforehand for predictable results.

JLCR:
https://jollylogic.com/products/chuterelease/

Eggtimer Apogee:
http://eggtimerrocketry.com/apogee_faqs/

 

[user 30299]

An altimeter-based Chute Release, which keeps the parachute bundled until you want it to open at a specified altitude.

You can use it with motor ejection or with a simple altimeter like the Eggtimer Apogee, to get the bundled chute out into the air.

Either way, it's still a learning curve that should be practiced beforehand for predictable results.

JLCR:
https://jollylogic.com/products/chuterelease/

Eggtimer Apogee:
http://eggtimerrocketry.com/apogee_faqs/

The Chute Release is definitely one of those items that requires a good bit of practice. One you learn how best
to set it up for your rockets, then it becomes a great tool in the recovery toolkit. Mine gets a lot of use with my
early builds that can't be converted into dual deploy.

 

[Lt72884]

What is JLCR?

this is the jolly logic chute release. Its great for a first time dual deploy. A little more expensive, but what cool about it, it can be used with even small model rockets for dual deploy.

It uses your main chute as the drogue chute in a way. You fold your main chute into a bundle, then wrap a band around it that goes into the jolly logic unit. as the rockets motor ejection pops the main out, you have this bundle slowing down the rocket and some what stabilizing it, then at a certain altitude, the JLCR releases the band allowing the chute to open up and land.

 

[wsume99]

That only makes sense if the practice rocket is cheaper or takes less time to build.

True or if the only rocket the has that can accept 38mm or larger motors is the L2 bird. When I built my L2 rocket it was the only one I had at the time that was capable of accepting L2 motors. I didn't want to destroy it learning DD so I used L1 rockets to practice DD first. The cost wasn't the driving concern for me. I didn't want to have to wait to built a new L2 rocket.

 

[wsume99]

How will I know my design is good and will work?

You can validate the design with rocksim or openrocket. Simulate the design in real world flight conditions to ensure it performs well. IMO it is not hard to design a rocket that will be stable and fly well. The tools are easy to use and there are lots of people here who can help you.

 

[user 30299]

Thank you for your detailed response and the images. You give me hope that this is a reasonable goal. That gives me an idea on how to adjust the sizing on my rocket as well. What did you use to annotate that drawing?

I see you used 6 centering rings. How did you come up with this number, and do you think I should increase my amount?

That design was done in AutoCAD. I lay out my builds in AutoCAD first to see how things fit together, what changes
I might want to make, etc. I rarely build kits these days. Most are my own design. Once I have the design the way
I want it then I'll move to RockSim or OpenRocket for the simulation.

As for the number of centering rings. Well, that was based on a calculated guess. You're relying on the rings and
the fins to hold the motor tube (motor) from going up through the middle of the rocket. Remember, I was planning
on putting some hard hitting motors in this rocket.

The rings are doubled up at the top for good anchorage of an eyebolt for the harness. The rings are doubled up at
the bottom to give solid anchorage of the motor tube to the fins and the body tube. There's a 1/2" space between
the end of the body tube and the start fin tab. Best to fill it with an extra centering ring.

There's a single centering ring at the top of the fin tab. This traps the fin tab between the rings and gives you
a solid structure to keep the motor from going up through the middle. The last single centering ring was for
good measure.

Here are pictures of the eyebolt and rings at the top of the motor tube. This gets epoxied, and then attached
to the motor tube.

 

[haon151]

You can validate the design with rocksim or openrocket. Simulate the design in real world flight conditions to ensure it performs well. IMO it is not hard to design a rocket that will be stable and fly well. The tools are easy to use and there are lots of people here who can help you.

Is there anything you see in my design that I should improve upon before taking the next step to build it?

 

[haon151]

That design was done in AutoCAD. I lay out my builds in AutoCAD first to see how things fit together, what changes
I might want to make, etc. I rarely build kits these days. Most are my own design. Once I have the design the way
I want it then I'll move to RockSim or OpenRocket for the simulation.

As for the number of centering rings. Well, that was based on a calculated guess. You're relying on the rings and
the fins to hold the motor tube (motor) from going up through the middle of the rocket. Remember, I was planning
on putting some hard hitting motors in this rocket.

The rings are doubled up at the top for good anchorage of an eyebolt for the harness. The rings are doubled up at
the bottom to give solid anchorage of the motor tube to the fins and the body tube. There's a 1/2" space between
the end of the body tube and the start fin tab. Best to fill it with an extra centering ring.

There's a single centering ring at the top of the fin tab. This traps the fin tab between the rings and gives you
a solid structure to keep the motor from going up through the middle. The last single centering ring was for
good measure.

Here are pictures of the eyebolt and rings at the top of the motor tube. This gets epoxied, and then attached
to the motor tube.

View attachment 573573 View attachment 573574

I like the doubling up idea for the eyebolt anchor point. I have heard some people use a Kevlar harness epoxied to the motor mount tube. What are the benefits and downsides to this approach compared to eyebolts?

One more question, do you have any recommendations on body material? I was thinking Quantum tubing but would like another opinion.

 

[user 30299]

I like the doubling up idea for the eyebolt anchor point. I have heard some people use a Kevlar harness epoxied to the motor mount tube. What are the benefits and downsides to this approach compared to eyebolts?

One more question, do you have any recommendations on body material? I was thinking Quantum tubing but would like another opinion.

Your questions have been discussed numerous times, and at length, on this Forum.

Just use the Search feature, and you can then whittle down the threads that you feel are most pertinent.

 

[wsume99]

Is there anything you see in my design that I should improve upon before taking the next step to build it?

Looks fine to me. It was stable throughout the flight on a J350 and a L1000 which pretty much covers the L2 motor spectrum. One thing to watch out for would be lower thrust, long burning motors that don't have enough power to meet the minimum launch rod velocity.

You have a 24oz mass object inside the coupler. Is that your avionics? That seems pretty heavy based on my experience. I would think you'd be closer to 12 oz with a full dual redundant setup. That is what mine are close to with two altimeters, two batteries and two switches. I lowered it to 12 oz in your model and everything was still stable so I wouldn't be worried. Just update the model with actual weights once you have them so you can get accurate simulations.

 

[haon151]

Looks fine to me. It was stable throughout the flight on a J350 and a L1000 which pretty much covers the L2 motor spectrum. One thing to watch out for would be lower thrust, long burning motors that don't have enough power to meet the minimum launch rod velocity.

You have a 24oz mass object inside the coupler. Is that your avionics? That seems pretty heavy based on my experience. I would think you'd be closer to 12 oz with a full dual redundant setup. That is what mine are close to with two altimeters, two batteries and two switches. I lowered it to 12 oz in your model and everything was still stable so I wouldn't be worried. Just update the model with actual weights once you have them so you can get accurate simulations.

Thank you for checking it over, I appreciate it. Yeah, I have heard launch velocity should be around 13-16 m/s at least. Will make sure to check this before choosing a motor.

That is my avionics. Was using estimated mass from SolidWorks. Obviously the materials don't match, so I will be sure to update with actual weights eventually.

Seems like I should be okay for a wide range of motors, except the really long L motors. Would I be too over stable for I motors? Some are over 3 cal, but will have to experiment with ones that will give me enough velocity off the rod.

 

[AfterBurners]

What is JLCR?

Jolly Logic Chute Release.

https://jollylogic.com/products/chuterelease/

 

[user 30299]

Is there anything you see in my design that I should improve upon before taking the next step to build it?

In your OR sim you show 6 ft. and 12 ft. recovery harnesses in the two payload areas.
Is that the actual setup for attaching a parachute and drogue?

Or did you do that just to give a nice looking representation in the OR graphics?

 

[haon151]

In your OR sim you show 6 ft. and 12 ft. recovery harnesses in the two payload areas.
Is that the actual setup for attaching a parachute and drogue?

Or did you do that just to give a nice looking representation in the OR graphics?

Yeah. Going to have 6 feet from the avionics bay to the drogue then 12 ft from the drogue to the booster section. This is the same in the main parachute bay as well.

 

[user 30299]

Yeah. Going to have 6 feet from the avionics bay to the drogue then 12 ft from the drogue to the booster section. This is the same in the main parachute bay as well.

Is it a single 18 ft. harness with an attachment point at 6 ft. for the chute?

Or are they two harnesses, 6 ft. and 12 ft.? If so, how are you attaching the harness ends and the chute at that common point?

 

[haon151]

Is it a single 18 ft. harness with an attachment point at 6 ft. for the chute?

Or are they two harnesses, 6 ft. and 12 ft.? If so, how are you attaching the harness ends and the chute at that common point?

Single 18 ft length. Knot tied 6 ft. from the end of the av bay which quicklink will attach to for the drogue. Still deciding between kevlar Y harness or eyebolt on the centering ring to attach the rest of the shock cord to the motor section. Another 18ft will be in the nose section with the same setup.

 

[thzero]

That design was done in AutoCAD. I lay out my builds in AutoCAD first to see how things fit together, what changes
I might want to make, etc. I rarely build kits these days. Most are my own design. Once I have the design the way
I want it then I'll move to RockSim or OpenRocket for the simulation.

As for the number of centering rings. Well, that was based on a calculated guess. You're relying on the rings and
the fins to hold the motor tube (motor) from going up through the middle of the rocket. Remember, I was planning
on putting some hard hitting motors in this rocket.

The rings are doubled up at the top for good anchorage of an eyebolt for the harness. The rings are doubled up at
the bottom to give solid anchorage of the motor tube to the fins and the body tube. There's a 1/2" space between
the end of the body tube and the start fin tab. Best to fill it with an extra centering ring.

There's a single centering ring at the top of the fin tab. This traps the fin tab between the rings and gives you
a solid structure to keep the motor from going up through the middle. The last single centering ring was for
good measure.

Here are pictures of the eyebolt and rings at the top of the motor tube. This gets epoxied, and then attached
to the motor tube.

View attachment 573573 View attachment 573574

Overkill

 

[user 30299]

Overkill

Thanks for the compliment! Much appreciated!

 

[user 30299]

Single 18 ft length. Knot tied 6 ft. from the end of the av bay which quicklink will attach to for the drogue. Still deciding between kevlar Y harness or eyebolt on the centering ring to attach the rest of the shock cord to the motor section. Another 18ft will be in the nose section with the same setup.

The kevlar and eyebolt will both work fine. Just ask yourself which is the easiest for you to actually put in place.

 

[wsume99]

Seems like I should be okay for a wide range of motors, except the really long L motors. Would I be too over stable for I motors? Some are over 3 cal, but will have to experiment with ones that will give me enough velocity off the rod.

I don't think you would have any problem at 3 cal. I don't have my sim files handy otherwise I'd check the ranges of stability I've actually flown but I don't see that as a problem. If you are that concerned about stability just add some weight aft of your CG. I don't believe I've ever heard of someone purposely adding "tail weight" before but that's how you would lower the stability.

 

[haon151]

The kevlar and eyebolt will both work fine. Just ask yourself which is the easiest for you to actually put in place.

Okay thank you. I'll probably just stick with the eyebolt then.

 

[haon151]

I don't think you would have any problem at 3 cal. I don't have my sim files handy otherwise I'd check the ranges of stability I've actually flown but I don't see that as a problem. If you are that concerned about stability just add some weight aft of your CG. I don't believe I've ever heard of someone purposely adding "tail weight" before but that's how you would lower the stability.

Great thanks. My mass of the avionics bay was probably overestimated. I'll be sure to double check everything once it's built and have the actual masses.

 

[user 30299]

Okay thank you. I'll probably just stick with the eyebolt then.

Be sure to use a "closed" eyebolt. See pictures below. The eye is welded closed. You can also use a forged eyebolt.

You can also see how the eyebolt is set at angle. This way it doesn't interfere with the body tube or a motor case
that extends beyond the motor tube. And you can still get a quick clip on to attach the harness.

 

[haon151]

Be sure to use a "closed" eyebolt. See pictures below. The eye is welded closed. You can also use a forged eyebolt.

You can also see how the eyebolt is set at angle. This way it doesn't interfere with the body tube or a motor case
that extends beyond the motor tube. And you can still get a quick clip on to attach the harness.

View attachment 574205 View attachment 574206

View attachment 574207

Yup, have been looking at some forged eyebolts on McMaster Carr.

How did you make sure that centering ring was completely level before epoxying it? Also, because I will have 3 centering rings, I won't have access to one side for internal fillets. What's your process for this?

 

[thzero]

https://www.rocketarium.com/ has some nice forged eyebolts in rocket sizes.

If I recall all the ones in McMaster were much too big

 

[Buster]

Having learned just about every discipline for L2 at my overly long L1 (and MPR) stage, and having gotten off my butt for my L2 two years ago, I'm going to go ahead and say that I agree with Handeman on his recommendations. I was comfortable with DD, having had over a hundred DD launches, and plenty of L1 launches on full size L1 motors in 4" birds.......so my L2 project was just another build, and my L2 launch was just another 'new rocket' launch.

Another reason for building a fully L2 capable bird is that my L1 was a beefed up MP rocket, and hardly suitable for flying any other L1 motors. I had to build another rocket to do that. I chose to build my L2 bird as a 'fully capable' instead of a one-off.

I did my L2 as a scratch built, 4" 54mm motor mount, full dual redundant DD with GPS in the nose. It's a rocket that I can fly from 1500ft to 8000ft comfortably to 'fly the field' and it will eat anything L2 in 38 or 54 that's installed in it. It's large enough to work on easily, large enough to see comfortably all the way up to 8K, and flexible enough to fly mid and large fields that are suited to L2 motors.

As to your question of needing GPS, that's a personal decision. Most of us can see a 4" rocket up to 6-8K, depends on paint and sky conditions. I think that 'altitude' is really only 50% the determining factor. Field conditions (trees/hills/scrub/line-of-sight to terrain) is at least 50% of it, too.
Bayboro (5 square miles of zero trees and soft plow or low crops) I don't see it as necessary up to about 10K, MDRA Higgs, with all it's trees and ditches and limited sight lines I use it 100% for anything going over 2K.
Similarly, soft plow or sod farm, usually not necessary, but let the beans or corn get over knee high and I use GPS nearly 100%. If you haven't experienced knee high crops eating even the largest of rockets yet, you're in for a real treat the first time you experience it!
Not mandatory, but saves a lot of angst when you can walk right up to it.

Or “tall cotton” 4-5 feet

 

[user 30299]

Yup, have been looking at some forged eyebolts on McMaster Carr.

How did you make sure that centering ring was completely level before epoxying it? Also, because I will have 3 centering rings, I won't have access to one side for internal fillets. What's your process for this?

Two good sources for the eyebolts are Chris Rocket Supplies and OneBadHawk. The prices are pretty good and the
shipping is usually fast. You are probably needing a 1/4" eyebolt for your rocket. The eyebolt in the picture is from
one of those sources. They usually include the nut and washers

If you plan on staying in this hobby or are working with a group, then order a few in assorted sizes for future builds.
In the pictures in my earlier post, #56, you can see I added a nut to the top of the eyebolt threads. This gives you a
solid stop for the top washer and maintains the extension of the eyebolt's shank. Just get the extra nut from your
local hardware store.

Yes, you can get internal fillets on the three centering rings. You can get fillets on all faces of the rings.
It's all about where you apply the epoxy, which direction you slide the rings onto the motor tube and
into the body tube, and the sequence of the build.

Please note, in the pictures below, the eyebolt was attached after the top centering ring was epoxied to the motor tube.

I applied a good bit of epoxy to the motor tube in the area just ahead of (to the left of the ring) and in
the ring's final location. Then I just slid the ring on, going from left to right (yellow arrows), as you see in
the 2nd picture. The first picture, blue arrow, shows the "natural" fillet that forms from the wiping action
of the ring. This also gets epoxy between the ring and the motor tube. You may want to give the ring
a twist/turn or two.



After the epoxy set overnight I came back and added a fillet on the ring's top face and also added the eyebolt.
I usually smear the epoxy all over the little bit of motor tube extension. Just to give it a little durability since
it's cardboard.

These next two pictures are not the best but you should get the idea. I stand the motor tube up on a level surface
and have spacers or blocking to keep the ring in place and level until the epoxy sets up. I'll use pieces of plywood
or other centering rings set out at the edge of the ring. Be sure to check the end of the motor tube for square
or "near square" (lol).



If you think about how the natural fillet is created, how does that influence (determine?) the epoxy and build sequence
for adding this motor tube to the body tube, the middle centering ring, the fins and then the bottom centering ring.

That natural fillet and build sequence will give you the internal fillets that you initially thought were not possible to add.